This invention relates to a stator structure of the type used in rotary machines, and more specifically, to structure within the compression section to guide working medium gases through the section.
An axial flow rotary machine, such as a gas turbine engine for an aircraft, has a compression section, a combustion section, and a turbine section. An annular flow path for working medium gases extends axially through the sections of the engine. The gases are compressed in the compression section to raise their temperature and pressure. Fuel is burned with the working medium gases in the combustion section to further increase the temperature of the hot, pressurized gases. The hot, working medium gases are expanded through the turbine section to produce thrust and to extract energy as rotational work from the gases. The rotational work is transferred to the compression section to raise the pressure of the incoming gases.
The compression section and turbine section have a rotor which extends axially through the engine. The rotor is disposed about an axis of rotation Ar. The rotor includes arrays of rotor blades which transfer rotational work between the rotor and the hot working medium gases. Each rotor blade has an airfoil for this purpose which extends outwardly across the working medium flow path. The working medium gases are directed through the airfoils. The airfoils in the turbine section receive energy from the working medium gases and drive the rotor at high speeds about an axis of rotation. The airfoils in the compression section transfer this energy to the working medium gases to compress the gases as the airfoils are driven about the axis of rotation by the rotor.
The engine includes a stator disposed about the rotor. The stator has an outer case and arrays of stator vanes which extend inwardly across the working medium flowpath. The stator extends circumferentially about the working medium flow path to bound the flow path. The stator includes seal elements for this purpose. An example is an inner shroud assembly having a circumferentially extending seal member (rubstrip) which is disposed radially about rotating structure and supported from. the vanes by an inner shroud. The rubstrip is in close proximity to the rotor structure to form a seal that blocks the leakage of working medium gases from the flowpath. The rubstrip for such shrouds may be formed of an elastomeric material. The elastomeric material may be disposed in uncured form on a metal, arcuate support surface. As the elastomeric material cures, the material bonds to the metal surface. The uncured elastomeric material is in fluid form (that is, assumes the shape of the container in which it is disposed) and is sticky. As a result, the uncured material may be difficult to handle and often requires extensive cleanup after use.
Examples of suitable candidate materials for use in high bypass commercial jet engines are injection molded thermoplastic materials which have been used for example in vane shrouds in exit guide vane and low-pressure compressor stator assemblies for approximately twenty years. Suitable elastomeric materials include silicone rubber which also has been in service during that period as an encapsulant to provide vane attachment and for damping functions.
However, a silicone rubber rubstrip supported by a substrate which is positioned by stator vanes or other structure must tolerate severe rubs from rotating structure. Such rubs may occur during normal operative conditions or abnormal operative conditions which might occur such as after an impact by a foreign object against the engine. The rubstrip must tolerate the severe rub without delaminating (a noncohesive failure) and moving into the flow path.
The above notwithstanding, scientists and engineers working under the direction of Applicants Assignee have sought to develop bonding systems for elastomeric materials, such as silicone rubber, for rubstrips used with stator vanes for the compression section of rotary machines with acceptable levels of durability and handling difficulty.
According to the present invention, a stator assembly is formed of a preformed circumferentially extending rubstrip which is bonded to an inner shroud by directly applying adhesives and primers between the shroud and the preformed rubstrip.
In accordance with one detailed embodiment, the shroud is a thermoplastic material, the rubstrip is preformed silicone rubber and an epoxy resin primer is provided for interacting with the thermoplastic material.
In accordance with another detailed embodiment, the preformed rubstrip is deflected radially inwardly during the method of making the assembly to cause the bond to extend in a vertical or spanwise direction to increase the shearing strength at the interface.
In accordance with one detailed embodiment, the inner shroud has a plurality of chambers bounded by the rubstrip and sealed by the bonding material and the chambers are in flow communication through one more openings with a source of pressurized gas for testing the strength of the bond between the rubstrip and the inner shroud.
According to the present invention, a method for bonding a preformed silicone rubber article to a thermoplastic substrate includes applying an epoxy resin primer to the substrate.
In accordance with one detailed embodiment of the present invention, the method includes applying a silicone rubber primer to the epoxy resin primer after curing the epoxy resin primer.
In accordance with a detailed embodiment, the epoxy resin primer contains a solvent which chemically reacts with the thermoplastic material.
A primary feature the present invention is a preformed rubstrip for a stator assembly. Another feature is a stator assembly, such as an inner shroud assembly, formed by bonding the preformed rubstrip to the inner shroud. In one embodiment, the shroud includes ribs. In one embodiment, a feature is a bond material for a preformed silicone rubber article and a thermoplastic substrate which includes epoxy resin and silicone rubber. A primary feature of the method includes curing the epoxy resin primer which is applied to a thermoplastic substrate prior to adding a layer of silicone rubber primer before bonding a silicone rubber article to the substrate.
An advantage of the present invention is the ease of making a shroud assembly by bonding a preformed elastomeric rubstrip to a shroud which results from not applying an uncured elastomeric material to the shroud. Another advantage is the bond strength that exists between a preformed silicone rubber rubstrip and the supporting inner shroud formed of thermoplastic material which results in part from the bonding material and, in one embodiment, from the bond material extending between axially facing surfaces on the shroud and on the rubstrip. In one embodiment, an advantage is the ability to nondestructively test the bond between a rubstrip and the shroud by pressurizing chambers bounded by the shroud and sealed by the bond material.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of the best mode for carrying out the invention and accompanying drawings.